1. Field of the Invention
The present invention relates to an IC card having an information recording medium for use in, for example, an ID card (identification card), a membership card, a prepaid card, a cash card, a commuter's pass and the like. More particularly, the present invention is concerned with an IC card having both recorded information of electronic data and visible information.
2. Description of Related Art
Conventionally, in ID cards for identifying individuals, a method for magnetically or optically reading information recorded has been widely used in a credit card and the like. However, the techniques are popularized and the data in the cards is easily altered or forged cards are spread, and there are increasing cases where people actually suffer damage from the forged cards. For this reason, in recent years, as means capable of controlling and protecting personal data, an IC card having an IC chip incorporated has drawn attention since it has a large data capacity and it can contain coded data.
Data to be recorded on an IC card is contained in an IC chip incorporated into the IC card. Therefore, for display or reading of the data recorded on the IC card, it is necessary to read the recorded data by means of a special reading apparatus, and therefore general users cannot read the data by themselves. For example, in membership cards in which a high premium or a point is put on members, inquiry by an information note or the like is separately required for if it is merely recorded onto the card. Further, when merely recording data onto a card of a commuter's pass, a means for reading the data is separately required.
There are increasing demands of easy display of the recorded data and, recently, for meeting the demands, a technique has been developed in which a polymer/low-molecule-type rewritable display medium, which contains an organic low molecule dispersed in a resin binder, and which achieves display by utilizing the opaque-transparent contrast, or a rewritable display medium, which contains a leuco compound and a color developing and erasing agent which reacts with the leuco compound dispersed in a resin binder, and which controls heat energy so that the leuco compound colors or erases the color, is provided as a rewritable display layer on the surface of a card. The above rewritable display layer is constituted by support, e.g., a plastic sheet, colored layer, recording (polymer/low-molecule or leuco compound, color developing and erasing agent) layer and protecting layer.
The rewritable display layer is formed on at least one surface of a shaped article having an IC module disposed between multilayered plastic sheets including two or more layers wherein the IC module has an IC mounted portion reinforced by a sealing resin or a reinforcing plate.
The IC module includes an IC chip mounted on an insulating substrate having an antenna coil, and the IC mounted portion of the IC module partially has a projection on the front and back surfaces due to the sealing resin or reinforcing plate provided thereon. For this reason, there is a problem in that the uneven surface of the IC module causes the card surface to be uneven during forming of the card and to lower the flatness and hence a spacing loss is caused between the rewritable display layer and a printing head during a printing operation, leading to an occurrence of print missing or slight touching, so that satisfied printing properties cannot be secured. Therefore, recently in the IC card production technique, it is very important to develop a method for securing favorable flatness of surface of the card after being formed.
As a conventional technique for improving the flatness of the card surface, for example, a structure of a card in which a through hole (relief hole) is formed in a plastic sheet stacked on an IC module in a region corresponding to the IC mounted portion so as to absorb the uneven surface of the IC module is described in patent document 1 shown below. In addition, a structure of a card in which the multilayered plastic sheet is improved in the combination of sheet thickness or the constituent materials to adjust the fluidity of the resins so as to absorb the uneven surface of the IC module is described in patent document 2 shown below.
[Patent Document 1]
    Japanese Patent Application Publication No. 2001-319210[Patent Document 2]    Japanese Patent Application Publication No. 2001-283175